This proposal, "The role of melanocytes in inner ear development," seeks to correlate the diminished presence of melanocytes in the inner ear with the lack of development, or an initiation of development followed by degeneration, as seen in pallid and mocha mice, respectively. A third mutant, muted has also been selected to study because of its phenotypic similarities with pallid and mocha. These coat color mutants are models for platelet pool storage deficiency and also share inner ear abnormalities. Attention will be focused on melanocytes for several reasons: 1) melanocytes are missing or in reduced numbers in inner ear structures of pallid and mocha mice; 2) melanocytes serve as a reservoir for manganese, an essential factor in carbohydrate synthesis required for otolith development; 3) supplementing the diet of pregnant females with manganese results in normal inner ear development in both pallid and mocha mice; and, 4) the gene (protein 4.2) responsible for the pallid phenotype is expressed at the melanosome membrane. The major goals of this proposal are to seek a better understanding of how protein 4.2, whose function is unknown, is involved in inner ear development and whether this information can be applied to two similar but discreet single gene mutations. This proposal describes a study of the expression of both protein 4.2 RNA and its protein product, pallidin, in developing fetal brain sections in order to document the migration and lack of migration in normal and mutant mice. Chemotactic profiles of cultured melanocytes may yield information concerning the ability of melanocytes from mutants to migrate from their neural crest origin to the site of inner ear induction. Hybridization with a cDNA probe for protein 4.2 under conditions of reduced stringency may provide clones of similarly acting cDNAs in mocha and muted. Finally, proteins from melanocytes of mocha and muted will be compared with their controls by polyacrylamide gel electrophoresis in an attempt to recognize and isolate the protein responsible for these mutations. Inner ear defects have been associated with several hereditary anomalies of pigmentation in several mammalian species, including human and mouse. Migration of melanocytes appears critical for normal induction, differentiation, and maintenance of inner ear structures. Information from this study, using these three mutations, should help clarify the role of melanocytes in this process.